1. Field of the Invention
The present invention relates to the production of stators for electrical machines and the like, and in particular it relates to a new and improved device for placing pre-wound coils into stator slots.
2. Prior Art
A known apparatus for inserting prewound coils into stator slots includes a star-shaped stripper member having in its outer periphery a series of longitudinal grooves, the said stripper member being movable parallel to its axis and slidable relative to elongated fingers located in said grooves.
Prewound coils are initially placed onto these figures as the latter extend through the centre of the stator. The stripper member is then moved to the centre of the stator, sliding along the fingers, to remove the coils from the fingers and insert the same into the stator slots. The end portions of the fingers which are opposite to the stator are housed in respective longitudinal grooves of a fixed hollow cylindrical finger holder, the grooves of said holder being aligned with the grooves of the stripper member.
An apparatus of this general type is disclosed in the U.S. Pat. No. 3,324,536, issued June 13, 1967. The device shown in this patent comprises an outer tubular housing provided with threaded bores in which screws are engaged for clamping each of the fingers in their respective grooves in the finger holder. Thus, the fingers are fixed relative to the holder, while the stripper member is slidable relative to the fingers. Therefore, in such known device, during the insertion procedure the wires of a coil frictionally engage the two adjacent fingers between which the coil is interposed. If the coil is large relative to the size of the space between the two adjacent fingers, the individual wires of the coil are jammed against each other as a result of this frictional engagement thereby pinching the coil. This happens if the diameter of the wire of the prewound coil is such that the angle of friction between two adjacent wires in the space between the two adjacent fingers is less than the critical angle of friction.
Numerous solutions for this problem have been proposed but none has been completely satisfactory. One such solution is to vary the size of the gaps between the fingers in dependence on the diameter of the wire to be inserted into the stator but this results in complications due to the need to replace the fingers when the diameter of the wire is to be varied.
A further solution is to form a stripper member in such a way that the coils are drawn rather than pushed thereby, but this leads to constructional complications and does not resolve the problem.
Another solution to the above-described problem is disclosed in the U.S. Pat. No. 3,559,268, issued February 2, 1971. This Patent is directed to a device of the above described general type, in which some of the fingers, preferably at least one finger of each couple of adjacent fingers between which a coil is interposed is fixed to the stripper member so as to slide axially therewith. Thus, since there is no sliding of the fingers which are fixed to the stripper member relative to the coil, there is no detrimental frictional engagement between the fingers and the coil. However, this solution still has the following drawbacks:
(a) the traction force exerted on the coils by the fingers fixed to the stripper member sometimes damages the varnish on the wire; PA0 (b) it is not possible, with this device, to insert several layers of wire simultaneously.